Pat the tuna steaks completely dry with paper towels. This is crucial for achieving a good sear.

In a small bowl, whisk together the sesame oil, olive oil, soy sauce, grated ginger, minced garlic, and black pepper. This will be your quick marinade and searing oil.

Heat a cast iron skillet or heavy-bottomed frying pan over medium-high heat until very hot. You want it to be hot enough to sear the tuna instantly.

Carefully place the tuna steaks into the hot skillet. Sear for 60-90 seconds per side for rare (cool red center), 90-120 seconds per side for medium-rare (warm red center). Adjust time based on thickness and desired doneness. Avoid overcooking, as tuna can become dry.

While the tuna is searing, you can spoon some of the oil mixture from the pan over the top of the steaks if desired.

Once seared to your liking, immediately remove the tuna steaks from the skillet and place them on a clean cutting board.

Let the tuna rest for 1-2 minutes before slicing. This allows the juices to redistribute.

Slice the tuna steaks against the grain into 1/2-inch thick pieces. Garnish with sesame seeds and sliced green onions, if using.